Inertial Sensor Assemblies (ISAs) require mechanical isolation for protection against mechanical shock and vibration. In a typical application, an ISA is fastened to a chassis. Without isolation, shock or vibration in the chassis becomes directly transmitted to the ISA, potentially damaging or degrading the performance of the ISA.
To isolate the ISA from shock and vibration, an isolation system is used. In general, an isolation system is a mechanical isolator that physically occupies the space between the ISA and the chassis. In the simplest case, the isolation system is rubber cushions that absorb vibration or shock occurring in the chassis, preventing its transmission to the ISA.
Isolation systems are classified by the frequency range in which they provide shock or vibration protection and by how they accomplish that protection. Two general classifications are active systems and passive systems.
Passive systems are generally composed of an elastomeric material. An elastomeric material and geometry is selected based on the frequency range of the shock or vibration that the system must insulate against. A soft elastomeric material provides protection over a wider frequency range, but with the trade-off of a greater mechanical displacement of the ISA. A stiffer elastomeric material insulates only against higher frequency shock and vibration, but with the benefit of a lower displacement of the ISA in the chassis. A significant benefit of elastomeric systems is that for certain isolator geometries, the isolator can be made to act isoelastically, meaning that for a given input the isolator can provide the same frequency response, and range of frequency response, in all three axes. An isolator geometry that offers isoelastic response is a cone-like shape.
A limitation of passive systems is that the frequency band in which they provide isolation is fixed. This limits the ability of a passive isolator to provide optimal isolation to systems used in environments having shock or vibration over a wide range of frequencies. The limitation requires that a compromise be made in the frequency range over which isolation protection can be provided. It also adds complexity to ISA systems because an ISA system must be customized to the environment in which it will used simply due to the isolation protection. It would be preferable if the isolation system could be generic, instead of having to individualize the ISA systems according to their isolation system and the environment that the ISA system is going to be used.
Active systems have an advantage in that they can respond to a varying frequency of vibration or shock by changing their stiffness. U.S. Pat. No. 7,261,834 is incorporated for reference, which explains the known art of magneto-rheological isolators. By being able to optimally insulate against a wide range of frequencies, active systems overcome two limitations of passive systems: 1) a compromised range of frequency protection; and 2) the need to customize isolation systems to the environment that they are used. Active systems have a further benefit of not needing to have their frequency response of individual isolators matched to one another, as in an ISA system that used multiple passive isolators.
A limitation of active systems, though, is system complexity and the number of axes to which they can respond. Somewhat simple active isolation systems exist, but they typically respond in only one axis. Three axis active isolation systems exist, but these are generally complex, expensive, and not compact.